Sheep uterine tissue is rich in the enzyme 5-lipoxygenase (5-LOX) that generates 5-hydroperoxyeicosatetraenoic acid (5-HPETE) on incubation with arachidonic acid (AA). The present study focuses on the ability of the enzyme 5-LOX to further act as 5, 6 leukotriene A4 (LTA4 ) synthase using 5-HPETE as a substrate. On incubation of 5-LOX with 5-HPETE and analysis of products on reversed-phase high-performance liquid chromatography, a prominent peak with a characteristic conjugated triene peak having absorption maxima of 261, 271, and 281 nm appeared. Based on cochromatography, the peak was identified as 5(S), 6(S)-dihydroxyeicosatetraenoic acid (5[S], 6[S]-diHETE), the non-enzymatic product of 5, 6 LTA4 . As the synthesis of 5,6-LTA4 from 5-HPETE requires 8-LOX activity, the present study demonstrates the dual LOX, 5- and 8-LOX activity for uterine 5-LOX, that is, 5-,6- LTA4 synthase in sheep uterus. In addition, endogenous 5,6-LTC4, the glutathione conjugate of 5,6-LTA4, was also observed in the sheep uterine homogenate, further demonstrating the synthesis of 5,6-LTA4 in the sheep uterine tissue.
Key words: Uterine 5-Lipoxygenase, 5-LOX, 5, 6-LTA4, 5(S),6(S)-diHETE, 5,6-LTC4
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